While it's theoretically possible for humans to visit a star beyond our own sun, the technology to accomplish such a trip doesn't exist and isn't close to being developed. In the 21st century humans don't yet have the ability to make the 93 million mile trip to the sun, our closest star. As a point of comparison, the next closest star is Proxima Centauri, which is multiple trillions of miles away.
While it's a daunting task, astronomers shy away from saying that anything is impossible. Instead, they start by focusing on how something could be done theoretically and then develop the practical means to accomplish that goal. The technology to take humans to Proxima Centauri is still very theoretical in the early 21st century. Using the least advanced of these technologies, the ion drive propulsion system, it would take humans about 80,000 years to reach Proxima Centauri.